In the same pan where you cooked the chicken, reduce the heat to medium-low, add a bit of vegetable oil along with the sesame oil.
Add the onion and cook it until soft, translucent and sweet in smell.
Add the garlic and ginger and cook them for a minute.
Add the cashews and the chicken from before and mix them in to warm them up.
Add the soy sauce and brown sugar. Let it simmer until it thickens slightly. Add te broccoli and mix it in.
Finish with the sesame seeds, spring onion and chilli flakes if you like them.